First-principles study of vacancy formation in LaNi(5)

Area of Science:

• Materials Science
• Solid-State Physics
• Computational Chemistry

Background:

• Lanthanum Nickel (LaNi(5)) is a key material for hydrogen storage applications.
• Understanding defect formation, such as vacancies, is critical for optimizing material performance and durability.
• Previous studies have suggested vacancy formation but lacked detailed site-specific analysis.

Purpose of the Study:

• To investigate the formation mechanisms and site preferences of nickel (Ni) vacancies in LaNi(5) using first-principles calculations.
• To correlate vacancy formation with changes in the material's lattice parameters.
• To determine the primary vacancy sites involved in the hydrogen absorption-desorption process.

Main Methods:

• First-principles electronic structure calculations were employed.
• Density Functional Theory (DFT) was used to model LaNi(5) and its defect structures.
• Vacancy formation energies were computed for different crystallographic sites.

Main Results:

• A clear site dependence was observed for Ni vacancy formation energies.
• The formation energy of a Ni vacancy at the 2c site is significantly lower (approx. 0.8 eV) than at the 3g site.
• Formation of Ni vacancies at 2c sites correlates with a decrease in lattice parameter 'a' and an increase in lattice parameter 'c', consistent with experimental observations during activation.

Conclusions:

• Nickel vacancies in LaNi(5) predominantly form at the 2c crystallographic sites.
• The preferential formation of Ni vacancies at 2c sites plays a crucial role in the structural changes observed during the hydrogen absorption-desorption cycling of LaNi(5).
• These findings provide fundamental insights into the degradation mechanisms of LaNi(5) and can guide the development of more stable hydrogen storage materials.